The ball-and-socket joint is an ideal connector joint for connecting two elements because of the capability of providing multi-directional angle adjustment between the two connected elements. When it is desirable to lock-in the adjusted angle between the connected elements, the structure of such a ball-and-socket requires certain changes. As shown in FIGS. 1 and 2, the basic structure of ball-and-socket joints includes a connecting unit 71, an encasing unit 72, and a fastening unit 73. Connecting unit 71 includes a ball-shaped connecting element 711. The top of encasing unit 72 includes a plurality of holding plates 721 forming a concave ball-shaped seat 722. Connecting element 711 of connecting unit 71 is placed in ball-shaped seat 722. The outer surface of holding plates 721 includes screw teeth 723 to be engaged with inner screw teeth 731 of fastening unit 73 for pressing and fastening holding plates 721 to connecting element 711 after connecting unit 71 and encasing unit 72 are adjusted to the desired angle. The ball-and-socket joint connector is widely applied in a plurality of products, such as back mirror in a vehicle, adjustable resting seat for mobile phones, and so on.
To reduce the manufacturing cost, the components of a conventional ball-and-socket joint are made of hard plastic, including connecting unit, encasing unit and fastening unit. A disadvantage of using the same hard plastic as the manufacturing material is that the lock-in effect is the result of friction between holding plates and the connecting element, which maybe insufficient to stay fastened when a large external force is applied to turn the ball-and-socket joint. Therefore, the weak fixation effect limits the utilization of this conventional structure. It is imperative to develop an enhanced structure that will improve the lock-in effect while maintaining the multi-directional angle adjustment capability.